For every barrel of crude oil produced, about three to ten barrels of water is produced. In the oil and energy industry, water that is drawn from the formation is referred to as “produced water.” The injection of steam for heavy oil recovery has become an important enhanced oil recovery (EOR) method. In EOR, high pressure steam is injected at a rate sufficient to heat the formation to reduce the oil viscosity and provide pressure to drive the oil toward the producing wells. For EOR, steam is normally produced in steam generators, with full steam makeup of water is required to feed the generator. The feed water should be substantially free of hardness, e.g., calcium and magnesium to prevent scale formation in the steam generator tubes or in the oil formation, causing plugging of downhole injection lines, causing increased pressure drop and increasing the power demand on pumps. Silica at high concentration can also pose a precipitation problem with scaling in steam generators and associated pipelines. Since fresh water is not always available for EOR, the treatment of produced water in the oil recovery process becomes necessary.
It is desirable to reduce the levels of silica and hardness to improve the efficiency of steam generators and simultaneously reduces the carbon generation to the atmosphere by reduction of natural gas consumption in the production of steam. Residual amount of free oil in the produced water also causes inefficiencies in the steam generators. Oil needs to be separated from the water for further processing, and such separation is a major issue in production operations. High efficiency reverse osmosis (“RO”) membranes reduce silica and hardness to negligible concentrations. The process desalinates the produced water—which further improves the quality of steam produced. However, reverse osmosis processes are energy intensive and generate significant pumping costs. The amount of free oil in water is a deterrent in steam generation processes, as it may cause significant fouling of reverse osmosis membranes. Materials that may undesirably serve to decrease reverse osmosis efficiency are free oil, dissolved organics, silica, magnesium ions and calcium ions.
There is a need for alternative and improved methods to treat produced water to avoid undesirable scale build-up within processing equipment.